This invention relates generally to inspection methods and particularly to a method of inspecting a pattern of elements on a working member.
Many products of industry are made by chemical etching processes. Examples of such products are integrated circuits and shadow masks for color television tubes. Typically, in the production of such parts, the material of which the part is to be made is covered with a coating of photosensitive material. A pattern of the part is photographically produced on the photosensitive material by exposing the material to light through the pattern, which is present on a rigid, transparent plate. The unexposed photosensitive material is washed away leaving the pattern on the bare part material. The pattern is chemically etched to remove or to lineate, the portion of the part material which has been made bare by washing away the unexposed photosensitive material. Typically, the pattern is photographically produced on the material by the use of a working member, or plate, upon which a very accurate pattern was previously produced. The working plate thus is used to produce a large number of parts. However, during use the working plate degradates and is worn and sometimes is damaged creating a need for replacement plates. For this reason, the working plates are produced from a precisely accurate master plate which is not used to produce parts. Prior to using the working plates to produce parts they are inspected to ensure that they are suitable for producing acceptable parts.
Presently, the working plates are inspected by using a scanner which projects a magnified image onto a viewing screen. Typically, the entire pattern can not be projected onto the screen and therefore the pattern moves across the viewing screen while an operator views the image. This method is subject to operator error because of the movement of the pattern across the screen. Also, for complicated patterns the inspection can require two to four hours leading to substantial operator fatigue. Operator error and fatigue frequently result in defects passing detection by the operator. For this reason, there is a need for a method of inspecting working plate patterns which is rapid and efficient in detecting all defects and which does not subject the operator to substantial fatigue. The invention fulfills these long felt needs.